1. Field of the Invention
The present invention relates to switches and, more particularly, relates to a non-contact switch using a magnetic sensor.
2. Description of the Related Art
Since a non-contact switch has no mechanical contact, there is no mechanical wear between contacts and it excels in durability. Also, since abrasion powder is not produced, it is suitable for application in foods and semiconductors. For example, in Japanese Unexamined Patent Publication No. 2005-326058, there is disclosed a door switch in which opening and closing of a commercial refrigerator door to be frequently opened and closed is detected by approach and separation of a magnet and a hall IC.
In the case where a non-contact switch is used as a door switch for a safety door which is for entering to and exiting from a work area where mechanical appliances such as industrial robots are surrounded by a safety fence, high reliability is required.
FIG. 7 shows a schematic configuration diagram of the non-contact switch suitable for the door switch for such safety door.
A non-contact switch 20 includes, for example, an actuator 21 serving as an operating member mounted on the door side to be opened and closed, and a switch body 22 which is mounted on the fixed frame side of the door and detects approach and separation of the actuator 21, that is, opening and closing of the door.
A plurality of magnets, four magnets 23-1 to 23-4 in this case, are arranged and incorporated in the actuator 21 along a longitudinal direction of a case 24; whereas, four hall ICs 25-1 to 25-4 serving as magnetic sensors are arranged and incorporated in the switch body 22 along the longitudinal direction of a case 26 so as to be opposed in a closed state of the door individually in response to the respective magnets 23-1 to 23-4. The four magnets 23-1 to 23-4 of the actuator 21 are arranged so as to be alternately different polarities between the neighboring magnets; whereas, the four hall ICs 25-1 to 254 of the switch body 22 are arranged so as to be respectively opposed to magnetic poles of one side of the respective magnets 23-1 to 23-4 in response to the polarities of the magnets 23-1 to 23-4 to be objects for detection. The respective hall ICs 25-1 to 254 give a detection output when the magnets 23-1 to 23-4 to be objects for detection are approached and entered to a detection region.
In such non-contact switch 20, it is regarded as that the door is closed when the approach of the four magnets 23-1 to 23-4 with different polarities arranged in a predetermined order is detected by the respective four hall ICs 25-1 to 254, that is, when the magnets 23-1 to 234 of corresponding polarities are detected by all four hall ICs 25-1 to 254; and a safety output with a high level is given to a higher safety controller. Then, it is regarded as that the door is not closed when the magnets 23-1 to 23-4 are not detected by any one of the hall ICs 25-1 to 25-4; and the safety output with the high level is not outputted.
The higher safety controller supplies power to mechanical appliances and drives the same only when the safety door is closed and the safety output with the high level is given from the non-contact switch 20 to the mechanical appliances arranged in a work area surrounded by the safety door and the safety fence and safety is secured.
In the non-contact switch 20 having the above configuration, for example, even if the switch 20 is tried to be nullified by approaching mere magnets to the switch body 22, magnetic fields of different polarities of a predetermined order cannot be detected by the four hall ICs 25-1 to 25-4; therefore, it is regarded as that the door is not closed, and the safety output is not outputted; and consequently, the mechanical appliances are not operated, and safety is secured.
In this manner, the plurality of the magnets 23-1 to 234 and the plurality of the hall ICs 25-1 to 25-4 are arranged and incorporated in the predetermined order in the actuator 21 and the switch body 22, respectively; and the safety output is not outputted unless the approach of the magnets 23-1 to 234 of corresponding polarities is detected by all the hall ICs 25-1 to 25-4 to enhance the reliability. However, the plurality of the magnets 23-1 to 23-4 and the plurality of the hall ICs 25-1 to 25-4 need to be arranged and incorporated in the cases 24 and 26; and therefore, reduction in size of the non-contact switch 20 is difficult.
That is, as compared with the case where magnetic lines of force of a single magnet 30 is detected by a hall IC 31 as shown in FIG. 8A, when the plurality of the magnets 30-1 and 30-2 are arranged, a reaching distance of magnetic lines of force is shortened as shown in FIG. 8B; and therefore, the narrower an interval of the plurality of the magnets 30-1 and 30-2 becomes, the shorter the reaching distance becomes. Therefore, in order to detect the approach of the magnets 30-1 and 30-2 in a constant detection distance by the hall ICs 31-1 and 31-2, the interval between the neighboring magnets 30-1 and 30-2 need to be above a certain level; and therefore, there is a limit to reduce the size in the arranged direction of the plurality of the magnets 23-1 to 234 and the plurality of the hall ICs 25-1 to 25-4.
The present invention has been made in view of the foregoing, and an object of the present invention is to provide a non-contact switch capable of reducing the size while securing the reliability.